Bio-based thermosetting bismaleimide resins using eugenol, bieugenol and eugenol novolac

5,5′-Bieugenol (BEG) and eugenol novolac (EGN) were synthesized by the oxidative coupling reaction of eugenol (EG) and the addition-condensation reaction of EG with formaldehyde, respectively. The EG, BEG and EGN were prepolymerized with 4,4′-bismaleimidediphenylmethane (BMI) at 180 °C and then compression-molded at finally 250 °C for 6 h to produce cured EG/BMI (EB), BEG/BMI (BB) and EGN/BMI (NB) resins with eugenol/maleimide unit ratios of 1/1, 1/2 and 1/3. The FT-IR analysis of EBs and 13C NMR analysis of the model reaction product of EG/N-phenylmaleimide (PMI) 1/3 at 200 °C for 12 h suggested that the ene reaction and subsequent Diels-Alder/ene reactions mainly occurred for EBs. The FT-IR analyses of BBs and NBs supported the occurrence of ene reaction and subsequent thermal addition copolymerization in a similar manner to the well-known curing reaction of 2,2′-diallylbisphenol A and BMI. The glass transition temperature (Tg) and 5% weight loss temperature (T5) of the cured resin increased with increasing BMI content, and EB 1/3 showed the highest Tg 377 °C and T5 475 °C. The flexural strengths and moduli of EBs and NBs were higher than those of BBs, and EB 1/2 showed the most balanced flexural strength and modulus (84.5 MPa and 2.75 GPa). The FE-SEM analysis revealed that there is no phase separation for all the cured resins.